<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #result {
            width: 200px;
            height: 100px;
            margin-top: 10px;
            background-color: #bfd;
        }
    </style>
</head>

<body>

    <!-- 需求: 点击发送/取消请求 -->
    <button>点击发送请求</button>
    <button>点击取消请求</button>
    <div id="result"></div>

    <script>
        const btn1 = document.getElementsByTagName('button')[0];
        const btn2 = document.getElementsByTagName('button')[1];
        const res = document.getElementById('result');

        let xhr = null;

        btn1.onclick = function () {
            xhr = new XMLHttpRequest();
            xhr.open('GET', 'http://127.0.0.1:8000/delay-server');
            xhr.send();
            xhr.onreadystatechange = function () {
                if (xhr.readyState === 4) {
                    if (xhr.status >= 200 && xhr.status < 300) {
                        res.innerHTML = xhr.response;
                    }
                }
            };
        };
        btn2.onclick = function () {
            // 取消请求
            xhr.abort();
        };

    </script>
</body>

</html>